1. Field of the Disclosure
The present disclosure relates generally to wireless communication systems and, more particularly, to signal delays between a baseband unit and a remote radio head in a wireless communication system.
2. Description of the Related Art
Wireless communication service providers typically are required to provide emergency call services (e.g. the e911 service in the U.S.) that are able to locate user equipment placing an emergency call to within a specified accuracy. For example, U.S. Federal Communication Commission (FCC) requirements specify that an emergency caller's location be determined within an accuracy of at least 50 meter (m) for 67% of calls and an accuracy of at least 150 m for 90% of calls. One technique for establishing the location of user equipment within the coverage area of a wireless communication system is Observed Time Difference Of Arrival (OTDOA), which uses the difference in arrival times of signals transmitted by multiple base stations to a user equipment to estimate the location of the user equipment by multilateration. Implementing OTDOA imposes stringent requirements on phase synchronization, delay measurements, and delay compensation in the base stations. For example, to achieve the FCC-mandated accuracy, transmission times of downlink radio frames from the antenna tip at a remote radio head should be known within 100 nanosecond (ns) accuracy. The end-to-end delay accuracy budget between a baseband unit and a remote radio head of the base station is therefore 100 ns.